Broadly speaking, there are two conventional modes used for creating video signals, the NTSC mode and the PAL mode, when image data expanded in frame memory is output to a display. However, recently, a video signal standard known as “CCIR REC 601 (referred to below as “REC 601”)” that can be used for both modes using the same hardware structure has become common.
A description will be given here using FIGS. 3 to 6 of a video signal output device that is based on REC 601. FIG. 3 is a block diagram showing the structure of a digital camera that uses a video signal output device that is based on REC 601. FIG. 4 shows the standards for the NTSC mode and the PAL mode. FIG. 5 shows the concept of the video signal timing in the NTSC mode. FIG. 6 shows the concept of the video signal timing in the PAL mode.
As is shown in FIG. 3, a digital camera 30 is provided with a video signal output section 36 that reads image data expanded in frame memory 35 has 640 pixels in a horizontal direction and 480 pixels in a vertical direction at a timing that corresponds to the video signal, and then adds the appropriate control signals and outputs a video signal. In addition, the video signal output section 36 is also formed with a variable magnification processing section 37 that serves as a video signal output device based on REC 601 by performing magnification alteration processing corresponding to either the NTSC mode or PAL mode on image data that has been expanded in the frame memory 35.
The image data expanded in the frame memory 35 may be image data input using a CCD 31, image data received via a communication section 32, or image data stored in an image data storage section 33. After the image data has undergone predetermined image processing in an image processing section 34, it is expanded in the frame memory 35. Moreover, video signals output from the video signal output section 36 may be displayed on a display section 40 such as an LCD (Liquid Crystal Display) or the like via an I/F section 38 and a display control section 39, or may be displayed on an external display device using a video signal OUT.
Next, a description will be given of the magnification alteration processing in the magnification alteration processing section 37. In REC 601 one pixel that is digitally specified by horizontal scanning and vertical scanning is not formed as a square. The reason for this is because in order to be able to handle both the NTSC mode and PAL mode standards shown in FIG. 4 using the same hardware structure and the same drive frequency, an intermediate frequency (13.5 MHz) is designated in which square pixels are formed in both modes.
Therefore, in the PAL mode, it is necessary to magnify the 480 lines in the vertical direction in the frame memory 35 to 576 effective display scan lines, and it is also necessary to magnify the 640 lines in the horizontal direction to 720 effective display clocks. Namely, when converting into a PAL mode video signal, magnification processing of 9/8 magnification in the horizontal direction and 6/5 magnification in the vertical direction is carried out in the magnification alteration processing section 37. Moreover, in the NTSC mode, it is necessary to magnify 640 lines in the horizontal direction into an effective display clock number of 720 clocks. Namely, when converting into a NTSC mode video signal, magnification processing of 9/8 magnification in the horizontal direction is carried out in the magnification alteration processing section 37.
In this way, in REC 601, magnification processing of 9/8 in the horizontal direction is normally carried out. Because the senses of a person are able to recognize a distortion of between approximately 3 to 5%, the 9/8 magnification processing is a necessary measure. Namely, if the 9/8 magnification processing is not carried out, a distorted image that has been contracted by 88.9% is displayed, which is sufficient distortion to be easily noticeable.
When the magnification alteration processing is performed, because in 9/8 magnification processing 8 pixels are increased to 9 pixels, interpolation magnification alteration processing is performed in which a filtering process is performed for 8 pixels so as to create the 9th pixel. Here, for a natural image such as image data obtained by photography using the CCD 31, because the image has smooth color changes, when the image is displayed after interpolation variable magnification processing, the resolution of the image is decreased, however, to the human eye there does not appear to be any distortion.
Next, a description will be given while referring to FIG. 7 of the outputting of a video signal by the video signal outputting section 36 to the display section 40 which displays images by overwriting ODD/EVEN fields in time shifts. FIG. 7 shows the concept of the lines when a display is made by overwriting in time shifts.
As is shown in FIG. 7, the CCD 31 inputs image data at a resolution of 320 lines in the horizontal direction and 240 lines in the vertical direction. The image processing section 34 expands the image data by altering the magnification thereof by a factor of 2 in both the vertical and horizontal directions (to a resolution of 640 lines in the horizontal direction by 480 lines in the vertical direction). The display section 40 then overwrites ODD/EVEN fields in time shifts. The result of this is that the image data is displayed at a resolution of 320 lines in the horizontal direction by 240 lines in the vertical direction.
The reason for the CCD 31 inputting the image data at a resolution of 320 horizontally and 240 vertically is because in monitoring mode it is necessary for the transfer load to be light and the display to be made in real time. Furthermore, the reason why the display section 40 overwrites ODD/EVEN fields in time shifts is because the resolution performance of the LCD of approximately 5 inches or less (i.e. the display section 40) used in monitoring mode is approximately 320 in the horizontal direction by 240 in the vertical direction.
However, in the above described conventional technology, various problems have occurred to do with the image quality of displayed images as is described below.
The first problem is that displayed graphic images become blurred. Namely, in the above conventional technology, because magnification alteration processing is always performed for graphic images created purely by data such as E-mail, WEB browsers, set screens, photography mode characters, times, photography numbers, and the like, these graphic images become blurred because of the filtering process.
The second problem is that when natural images are displayed on the NTSC mode display section 40 using PAL mode video signals, the image quality is deteriorated. Namely, because the majority of display sections 40 have the NTSC mode pixel layout (because the 480 lines in the vertical direction are displayed progressively, this comes to approximately 90% of 240 lines—i.e. of half of the 480 lines) due to the demands of the marketplace and the like, the number of lines is absolutely insufficient for video signals in the PAL mode that require 288 lines. Consequently, in the above conventional technology, when natural images are displayed on the NTSC mode display section 40 using PAL mode video signals, although the 5/6 magnification alteration processing in a straight direction is performed in the display section 40, the magnification alteration processing by the magnification alteration processing section 37 does not take into account the magnification alteration processing by the display section 40. Therefore, the image quality is deteriorated due to the repeated magnification alteration processings.
The third problem is that when image data stored in the image data storage section 33 or the like is displayed, it is difficult for this to be displayed on the display section 40 in a short time. Namely, the image data input from the CCD 31 in a high definition (i.e. high pixel number) digital camera, which have become common in recent years, greatly exceeds the number of pixels required for the video signal standard (640 horizontally by 480 vertically). For example, image data having 1280×960 pixels or 1600×1200 pixels is stored in the image data storage section 33 as a main photograph image. If, however, the image data is not to be used as data, but is instead to be displayed on an external display device via the device display section 40 and the video signal OUT, a resolution of 640 in the horizontal direction and 480 in the vertical direction is sufficient. Therefore, in the above conventional technology, the image data of the main photograph image is reduced in the image processing section 34 and expanded in the frame memory 35 and magnification alteration processing is normally performed on the expanded image data in the magnification alteration processing section 37. As a result, it is difficult to display the image data in a short time.
The fourth problem is that it is difficult to confirm framing from an image displayed on the display section 40. Namely, the current situation is that in order for the non-effective range to not be displayed, only 90% or so of the effective display range of the display section 40 is displayed. However, in the above conventional technology, because the magnification alteration processing section 37 always performs the magnification alteration processing to match the number of scan lines of the display section 40, the reality is that it is not possible to display all of the image data expanded in the frame memory. Therefore, it is not possible to display 100% of photographed image data or of an image when monitoring or the like which makes it difficult for framing to be confirmed.
The fifth problem is that when ODD/EVEN fields are overwritten in time shifts, there is a possibility that appropriate overwriting will not be carried out. Namely, when image data is magnified vertically and horizontally by a factor of 2 and expanded in the frame memory 35 as a pair, while it is necessary for this pair to be overwritten in time shifts as a pair once again on the display section 40, there may be a wrong positioning of one line depending on the specifications of the display section 40, in which case the appropriate overwriting is not carried out.